This invention relates generally to the field of devices and methods for the rehabilitation and/or lining of pipes or other tubular members wherein a polymer resin or similar uncured polymer material is sprayed onto the interior wall of the pipe, the sprayed material curing to form a layer possessing desirable properties, such as liquid impermeability, elasticity, rigidity, corrosion resistance, etc. The lining layer may be applied directly to the pipe wall itself, or successive layers may be applied to create multiple layers. The invention relates to such devices which comprise a sprayer mechanism that is transported along the interior of the pipe, the sprayer mechanism typically comprising a rotating member that distributes the uncured polymer as it moves linearly along the pipe. More particularly, the invention relates to measuring devices and methods that measure the thickness of the polymer layer applied to the exposed inner surface.
The structural integrity of pipe lining relies on the lining thickness, which makes consistent lining thickness one of the key parameters defining the quality of lining. In Class I and Class II linings (corrosion or ‘barrier’ coatings) this may not be all that critical, however, in Class III and IV, the structural augmentation is directly reliant on consistent liner thickness. Irregularities in the liner thickness will pave the way for high stress concentration regions, leading to the origin of anomalies in the form of cracks and perforations, which over a period may result in the complete failure of the pipe. Additionally, these pipe failures can lead to huge amount of potable water loss, soil erosion, sink holes in streets, catastrophic and dramatic consequences to the environment and human life if the pipeline effluent is hazardous.
As per the current AWWA and ASTM lining standards, the thickness of the liner applied to the pipe internal wall is verified by one of the following three methods:
First, a Wet Film Thickness Gauge or Ultrasonic Measurement device is used at the two ends of the lined pipe. In this method, the Ultrasonic Device and Wet Film Thickness Gauge can only record the measurements at the pipe ends, only as far as the operator can reach into the pipe while still being able to read the instrument. It is not capable of measuring the thickness at points in the interior of the pipe.
Second, to be able to measure the thickness on multiple long run pipe, the standard is to remove by excavation one small section of pipe in the center of a lining segment for every 2500 feet of pipe lined. This only provides thickness measurements at intermittent regions, not continuously throughout the length of the pipe. For example, if a typical Sprayed-In-Place-Pipe (SIPP) lining application is along a segment of about 500 feet of pipe, the operator is only testing the thickness at each end of the pipe (method 1) and in the middle with excavation and removal of approximately 20 feet of pipe (method 2), so the minimum distance in which no thicknesses are verified can be roughly 480 feet. The issue with all of these ‘post’ lining thickness verification methods is that there is no way to determine the thickness of the lining in between the measurement points. These standards requirements simply ‘assume’ that if the lining thickness is correct at both ends or the center then it is correct throughout the pipe. When considering the discontinuities in old worn pipe that directly impede the mechanical efficacy of the lining device, this assumption is simply baseless and without merit.
In a third method to measure the liner thickness along the entire length of pipe, a robotic ultrasound device travels the entire length of pipe and takes readings of the lining thickness after the pipe has been lined and cured. These units are expensive, as well as being highly unreliable and inaccurate.
The main problem with all of these post-cure lining thickness verification methods is that it only informs the operator of a lining thickness fault after the lining has already been applied on the pipe and liner application equipment has been removed. In the event that the lining thickness does not meet specification or requirements the pipe has to be lined again, which is expensive and time consuming. Another issue is that many of the polymerics have a short ‘recoat window’ so additional lining may not adhere to the existing lining resulting in failure if the time gap between curing and relining is too great.
It is an assumption within the industry that the liner operator is capable of accurately predetermining liner thickness by performing a simple calculation based on pipe diameter, lining device speed and material flow. These three inputs are used to determine liner thickness under the misguided premise that if you know the diameter, speed and flow then you can determine the final lining thickness. There is no account in this calculus whether the lining material is applied in a consistent thickness circumferentially in the pipe or not. While there might be enough material cast inside the pipe at any given point to form a layer, the material may very well be thicker on one side of the pipe than the other, and there is also a possibility of material being slumped into the pipe due to gravity. Currently in the SIPP industry the above-mentioned means of thickness verification are the only means available due to the mechanical functionalities of the lining apparatuses available.
To be able to able to verify the consistency of lining thickness it is essential to have a reliable and accurate method of measuring the lining thickness which can record the measurements with high precision and repeatability, and yet be economical in terms of cost. The object of this invention is to address the above challenges associated with accurate lining thickness measurement by providing a cost effective, reliable and accurate method to measure the thickness of the lining material casted on the host pipe in real time, i.e., virtually simultaneously with the application of the liner material.